This invention relates to a process for reclaiming vulcanized rubber, to the soluble reclaimed rubber thus produced, and to shaped articles of rubber which contain substantial amounts of the soluble reclaimed rubber.
In recent years the problem of disposing of worn-out tires has become acute. A number of suggestions have been made for their disposal. For example, scrap tires have been disposed of by open-burning which resulted in intolerable heavy pollution of the environment. Non-polluting incineration of scrap tires is possible; however, this method is viewed only as a matter of expediency and is basically wasteful of a rather valuable raw material. Incineration with waste-heat recovery to generate steam is still another improvement in technology to utilize worn-out tires. However, this latter procedure is not a true recycle technology and again can be considered as wasteful of a rather valuable raw material.
U.S. Pat. No. 3,674,433 shows heating of ground scrap rubber in a carbon-black feedstock oil and use of the mixture to produce carbon black. Here again no true recycling is shown.
Few practical methods have been suggested for recycling worn-out tires which would incorporate them in the manufacture of new tires or other new rubber products.
Reclaiming of scrap rubber has been practiced for many years, with digestion and separation of textile materials, and some "de-vulcanization" and degradation of the polymer. Recent increases in processing costs have made these operations uneconomical, however, and many plants have discontinued operation. One of the most expensive steps in conventional reclaiming is concerned with removal of textile fabrics from the scrap. Acid or alkali treatments have been used, together with physical separation of fibers, as by blasts of air or steam. To expedite removal of textile fibers, considerable cost is incurred in size-reduction of the scrap rubber feed, since the tire carcass scrap must be in small particles to allow for fiber removal.
Besides worn-out tires, another disposal problem is presented by defective tires which must be scrapped by the manufacturer. Because of their different chemical and physical nature, they cannot be processed "as is" in conventional reclaiming operations but must be allowed to age in outdoor storage for several years. The storage requirements thus pose an additional problem in reclaiming reject tires of this type.
Thus, the need exists for a reclaiming process which would permit inexpensive recycling of scrap tires to incorporate the valuable rubber they contain into new rubber articles. A reclaimed rubber which is in a form for easy handling and processing is also a desirable goal. Finally, the use of a cost-reducing compounding ingredient in rubber which will improve the processing and handling of the rubber, yet not impair the properties of the finished rubber article is of obvious advantage.